Development and characterization of magnetic nanoparticles Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ (0 $\le x\le$ 0.6) for biomedical applications

The results of studies of the properties of co-deposition of magnetic nanoparticles (MNPs) of Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ spinel ferrites synthesized (at $x$ = 0.0; 0.1; 0.2; 0.4; 0.6) in order to synthesize magnetic particles for biomedical applications. X-ray diffraction (XRD), raman spectra, magnetic measurements and Mossbauer spectroscopy (MS) were used to study the Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ MNPs. It was found that the synthesized MNPs Co$_x$Zn$_{1-x}$Fe$_2$O$_4$ are single-phase. According to the results of XRD measurements, it was found that the average sizes of crystallites are 13 nm for CoFe$_2$O$_4$ ($x$ = 0) and, with an increase in the Zn concentration, they decrease to 7 nm for Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ ($x$ = 0.6), which is consistent with the Mossbauer data, which showed that the sizes of crystallites vary from 14 to 8 nm. In the raman spectra of the Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ MNPs in the region of $\sim$ 620 cm$^{-1}$, splitting of the $A_{1g}$, line is observed, indicating that the studied particles have an inverse spinel structure. The change in the ratio between intensities of $A_{1g}$ (1) and $A_{1g}$ peaks is indicative of a significant redistribution of Co$^{2+}$ and Fe$^{3+}$ cations between tetrahedral andoctahedral positions in Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ MNPs as the quantity of Zn increases, which is confirmed by the Mossbauer data. It is found that small sizes of MNPs result in a strengthening of the effects of size and an effect of surface on the magnetic structure of the surface layer. The MS analysis has shown that there is a layer on the MNP surface, the magnetic structure of which is different from from the structure of the crystallite volume. With increase in the quantity of Zn ions thickness of this layer increases and at $x$ = 0.6 the particle becomes completely paramagnetic. Mossbauer studies have shown that Co$_{0.8}$Zn$_{0.2}$Fe$_2$O$_4$ ($x$ = 0.2) particles are inthe superparamagnetic state and theirmagnetic blocking temperature is $\sim$ 315 K, which is the most acceptable for the treatment of cancer by the magnetic hyperthermia method.